U.S. patent application number 15/432453 was filed with the patent office on 2017-08-03 for high rate deposition systems and processes for forming hermetic barrier layers.
The applicant listed for this patent is Corning Incorporated. Invention is credited to Robert Alan Bellman, Ta-Ko Chuang, Robert George Manley, Mark Alejandro Quesada, Paul Arthur Sachenik.
Application Number | 20170218503 15/432453 |
Document ID | / |
Family ID | 50772311 |
Filed Date | 2017-08-03 |
United States Patent
Application |
20170218503 |
Kind Code |
A1 |
Bellman; Robert Alan ; et
al. |
August 3, 2017 |
HIGH RATE DEPOSITION SYSTEMS AND PROCESSES FOR FORMING HERMETIC
BARRIER LAYERS
Abstract
A method of forming a hermetic barrier layer comprises
sputtering a thin film from a sputtering target, wherein the
sputtering target includes a sputtering material such as a low
T.sub.g glass, a precursor of a low T.sub.g glass, or an oxide of
copper or tin. During the sputtering, the formation of defects in
the barrier layer are constrained to within a narrow range and the
sputtering material is maintained at a temperature of less than
200.degree. C.
Inventors: |
Bellman; Robert Alan;
(Painted Post, NY) ; Chuang; Ta-Ko; (San Jose,
CA) ; Manley; Robert George; (Vestal, NY) ;
Quesada; Mark Alejandro; (Horseheads, NY) ; Sachenik;
Paul Arthur; (Corning, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Corning Incorporated |
Corning |
NY |
US |
|
|
Family ID: |
50772311 |
Appl. No.: |
15/432453 |
Filed: |
February 14, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13840752 |
Mar 15, 2013 |
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15432453 |
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61731226 |
Nov 29, 2012 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C23C 14/541 20130101;
C23C 14/35 20130101; C23C 14/10 20130101; C23C 14/34 20130101 |
International
Class: |
C23C 14/35 20060101
C23C014/35; C23C 14/54 20060101 C23C014/54; C23C 14/10 20060101
C23C014/10 |
Claims
1. A method of forming a hermetic barrier layer, comprising:
providing a substrate and a sputtering target within a sputtering
chamber, the sputtering target including a thermally conductive
backing plate and a sputtering material comprising glass;
maintaining the substrate at less than 23.degree. C. during
sputtering; and forming a self-passivating barrier layer comprising
the sputtering material over a surface of the substrate at a
deposition rate of about 10 .ANG./sec or greater by actively
cooling the sputtering target at less than about 200.degree. C. and
sweeping the sputtering target with an ion beam at near normal
incidence, wherein the self-passivating layer has a defect size
distribution and defect density distribution less than a critical
self-passivation threshold such that defect diffusion paths are
sealed through molar volume expansion of less than 10% of the
sputtering material when exposed to air or moisture.
2. The method of claim 1, wherein the sputtering material more
specifically comprises low T.sub.g glass, a precursor of a low
T.sub.g glass, and/or an oxide of copper or tin.
3. The method of claim 2, wherein the sputtering material is
selected from the group consisting of phosphate glasses, borate
glasses, tellurite glasses, and/or chalcogenide glasses.
4. The method of claim 3, wherein the sputtering material more
specifically comprises a material selected from the group
consisting of a tin phosphate, tin fluorophosphate and a tin
fluoroborate.
5. The method of claim 3, wherein composition of the sputtering
material comprises: 20-100 mol % SnO; 0-50 mol % SnF.sub.2; and
0-30 mol % P.sub.2O.sub.5 or B.sub.2O.sub.3.
6. The method of claim 1, wherein, during the forming of the
self-passivating barrier layer, internal pressure of the chamber is
maintained less than 10.sup.-3 Torr.
7. The method of claim 1, further comprising cooling the substrate
to a temperature less than room temperature.
8. A method of forming a hermetic barrier layer, comprising:
providing a substrate and a sputtering target within a sputtering
chamber, the sputtering target including a thermally conductive
backing plate and a sputtering material selected from at least one
of a low Tg glass with a glass transition temperature of less than
about 400.degree. C. or a precursor of the low Tg glass;
maintaining the substrate at less than 23.degree. C. during
sputtering; and forming a self-passivating barrier layer comprising
the sputtering material over a surface of the substrate at a
deposition rate of about 10 .ANG./sec or greater by actively
cooling the sputtering target at less than about 200.degree. C. and
sweeping the sputtering target with an ion beam at near normal
incidence, wherein the self-passivating layer has a defect size
distribution and defect density distribution less than a critical
self-passivation threshold such that defect diffusion paths are
sealed through molar volume expansion.
9. The method of claim 8, wherein the molar volume expansion is of
less than 15% of the sputtering material when exposed to air or
moisture.
10. The method of claim 9, wherein the molar volume expansion is of
less than 10% of the sputtering material when exposed to air or
moisture.
11. The method of claim 8, wherein the molar volume expansion is
from 1% to 15% of the sputtering material when exposed to air or
moisture.
12. The method of claim 8, wherein, during the forming of the
self-passivating barrier layer, internal pressure of the chamber is
maintained less than 10.sup.-3 Torr.
13. The method of claim 8, wherein the sputtering material is
selected from the group consisting of phosphate glasses, borate
glasses, tellurite glasses, and/or chalcogenide glasses.
14. The method of claim 13, wherein the sputtering material more
specifically comprises a material selected from the group
consisting of a tin phosphate, tin fluorophosphate and a tin
fluoroborate.
15. A method of forming a hermetic barrier layer, comprising:
providing a substrate and a sputtering target within a sputtering
chamber, the sputtering target including a thermally conductive
backing plate and a sputtering material selected from at least one
of a low Tg glass with a glass transition temperature of less than
about 400.degree. C. or a precursor of the low Tg glass;
maintaining the substrate at less than 23.degree. C. during
sputtering; and forming a self-passivating barrier layer comprising
the sputtering material over a surface of the substrate by actively
cooling the sputtering target at less than about 200.degree. C. and
sweeping the sputtering target with an ion beam at near normal
incidence, wherein the self-passivating layer has a defect size
distribution and defect density distribution less than a critical
self-passivation threshold such that defect diffusion paths are
sealed through molar volume expansion of less than 15% of the
sputtering material when exposed to air or moisture.
16. The method of claim 15, wherein the sputtering material is
selected from the group consisting of phosphate glasses, borate
glasses, tellurite glasses, and/or chalcogenide glasses.
17. The method of claim 16, wherein the sputtering material more
specifically comprises a material selected from the group
consisting of a tin phosphate, tin fluorophosphate and a tin
fluoroborate.
18. The method of claim 15, wherein, during the forming of the
self-passivating barrier layer, internal pressure of the chamber is
maintained less than 10.sup.-3 Torr.
19. The method of claim 15, further comprising cooling the
substrate to a temperature less than room temperature.
20. The method of claim 15, wherein the molar volume expansion is
of less than 10% of the sputtering material when exposed to air or
moisture.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 13/840,752, filed on Mar. 15, 2013, which
claims the benefit of priority under 35 U.S.C. .sctn.119 of U.S.
Provisional Application Ser. No. 61/731,226 filed on Nov. 29, 2012,
the contents of which are relied upon and incorporated herein by
reference in their entireties.
BACKGROUND
[0002] The present disclosure relates generally to hermetic barrier
layers, and more specifically to sputtering targets and
high-throughput physical vapor deposition methods for forming
hermetic barrier layers.
[0003] Hermetic barrier layers can be used to protect sensitive
materials from deleterious exposure to a wide variety of liquids
and gases. As used herein, "hermetic" refers to a state of being
completely or substantially sealed, especially against the escape
or entry of water or air, though protection from exposure to other
liquids and gases is contemplated.
[0004] Approaches to creating hermetic barrier layers include
physical vapor deposition (PVD) methods such as evaporation or
sputtering, and chemical vapor deposition (CVD) methods such as
plasma-enhanced CVD (PECVD). Using such methods, a hermetic barrier
layer can be formed directly over the device or material to be
protected. Alternatively, hermetic barrier layers can be formed on
an intermediate structure such as a substrate or a gasket, which
can cooperate with an additional structure to provide a
hermetically-sealed workpiece.
[0005] Both reactive and non-reactive sputtering can be used to
form a hermetic barrier layer, for instance, under room temperature
or elevated temperature deposition conditions. Reactive sputtering
is performed in conjunction with a reactive gas such as oxygen or
nitrogen, which results in the formation of a corresponding
compound barrier layer (i.e., oxide or nitride). Non-reactive
sputtering can be performed using an oxide or nitride target having
a desired composition in order to form a barrier layer having a
similar or related composition.
[0006] On the one hand, reactive sputtering processes typically
exhibit faster deposition rates than non-reactive processes, and
thus may possess an economic advantage in certain methods. However,
although increased throughput can be achieved via reactive
sputtering, its inherently reactive nature may render such
processes incompatible with sensitive devices or materials that
require protection.
[0007] Economical sputtering materials, including sputtering
targets that can be used to protect sensitive workpieces such as
devices, articles or raw materials from undesired exposure to
oxygen, water, heat or other contaminants are highly desirable.
SUMMARY
[0008] Disclosed herein are methods for preparing sputtering
targets comprising low melting temperature (LMT) glass compositions
and attendant methods for high-rate deposition of thin barrier
layers exhibiting a self-passivating attribute. Operating
conditions are selected to limit the surface temperature of the
target during sputtering while providing for the formation of a
deposited barrier layer having a small size as well as a small
number density of individual defects such as pinholes. In
embodiments, the number density and defect size is constrained to
lie below a critical threshold.
[0009] In accordance with various embodiments, self-passivating
barrier layers comprising low melting temperature glass
compositions can be formed at relatively high throughput (high
deposition rate) by, inter alia, lowering the sputtering chamber
background pressure, precisely controlling the substrate and
sputtering target temperature, sweeping the energy source (e.g.,
plasma) that engages the sputtering target, and limited the flux of
sputtered material to a narrow angle.
[0010] A method of forming a hermetic barrier layer comprises
providing a substrate and a sputtering target within a sputtering
chamber, maintaining the sputtering material at less than
200.degree. C., and sputtering the sputtering material with a power
source to form a barrier layer comprising the sputtering material
over a surface of the substrate. The sputtering target includes a
sputtering material formed over a thermally conductive backing
plate. The sputtering material may include a low T.sub.g glass, a
precursor of a low T.sub.g glass, or an oxide of copper or tin.
[0011] The power source may include an ion source, a laser, plasma,
a magnetron or combinations thereof. For example, the sputtering
may comprise ion beam-assisted deposition. A further example may
include a remote plasma generation sputter system that features
independent (non-coupled) control of ion generation and density at
the source, as well as control of the ion current, and voltage
biasing to the target.
[0012] During formation of the barrier layer, the power source may
be translated with respect to the sputtering target and/or the
sputtering target may be rotated. In addition to maintaining the
sputtering material at less than 200.degree. C., the substrate may
be maintained at less than 200.degree. C. Hermetic barrier layers
can be formed using the disclosed process at a deposition rate of
at least 10 A/sec.
[0013] Sputter conditions are chosen to ensure the defect size and
density distributions in the deposited layer are sufficiently small
that defect diffusion paths can be effectively sealed upon exposure
to moisture or oxygen. Sealing proceeds by virtue of the deposited
layer's self-passivating attribute. We have shown that inorganic
oxides exhibiting a molar volume expansion of from 1% to 15% upon
reaction with water or oxygen are candidates for hermetic barrier
layer formation.
[0014] Passivation may occur "passively" by simple exposure to
ambient conditions, or "actively" by submerging the barrier layer
in a water bath or exposing it to steam. The average defect size
and density may be less than the expansion associated with the
molar volume expansion of the as-deposited layer that accompanies
passivation. Deposition conditions are used to ensure the defect
size and density distributions within the barrier layer result in a
population of void spaces that can be sealed from the molar volume
expansion.
[0015] Additional features and advantages will be set forth in the
detailed description which follows, and in part will be readily
apparent to those skilled in the art from that description or
recognized by practicing the invention as described herein,
including the detailed description which follows, the claims, as
well as the appended drawings.
[0016] It is to be understood that both the foregoing general
description and the following detailed description present
embodiments of the invention, and are intended to provide an
overview or framework for understanding the nature and character of
the invention as it is claimed. The accompanying drawings are
included to provide a further understanding of the invention, and
are incorporated into and constitute a part of this specification.
The drawings illustrate various embodiments of the invention and
together with the description serve to explain the principles and
operations of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a plot of magnetron sputter deposition rate versus
power;
[0018] FIG. 2 is a plot of magnetron sputter deposition rate and
barrier layer uniformity versus substrate-target distance;
[0019] FIG. 3 is a schematic diagram of a single chamber sputter
tool for forming hermetic barrier layers;
[0020] FIG. 4 is a Thornton diagram depicting various barrier layer
microstructures;
[0021] FIG. 5 is a plot of barrier layer composition versus
deposition rate for different magnetron sputtering conditions;
[0022] FIG. 6 is a plot of Sn.sup.4+ content versus deposition rate
for a niobium-doped tin fluorophosphate glass material;
[0023] FIG. 7 is an illustration of a hermetic barrier layer formed
over a surface of a substrate;
[0024] FIG. 8 depicts a portion of an RF sputtering apparatus
according to an example embodiment;
[0025] FIG. 9 depicts a portion of a continuous in-line magnetron
sputtering apparatus according to a further example embodiment;
[0026] FIG. 10 in an illustration of a calcium-patch test sample
for accelerated evaluation of hermeticity;
[0027] FIGS. 11A-11F show test results for non-hermetically sealed
(left, FIGS. 11A-11C) and hermetically sealed (right, FIGS.
11D-11F) calcium patches following accelerated testing;
[0028] FIGS. 12A-12D show glancing angle (FIG. 12A, FIG. 12C) and
thin film (FIG. 12B, FIG. 12D) x-ray diffraction (XRD) spectra for
a hermetic CuO-based barrier layer-forming material (top series)
and a non-hermetic Cu.sub.2O-based barrier layer forming material
(bottom series);
[0029] FIGS. 13A-13I show a series of glancing angle XRD spectra
for hermetic CuO-based barrier layers following accelerated
testing;
[0030] FIGS. 14A-14B are series of glancing angle XRD spectra for
hermetic SnO-based barrier layers (FIG. 14A) and non-hermetic
SnO.sub.2-based barrier layers (FIG. 14B) following accelerated
testing;
[0031] FIG. 15 is a photograph of a copper backing plate according
to various embodiments;
[0032] FIG. 16 is a photograph of a solder-coated copper backing
plate;
[0033] FIG. 17 is an image of an example sputtering target
comprising an annealed low T.sub.g glass material;
[0034] FIG. 18 in an image of a pressed low T.sub.g glass
sputtering target;
[0035] FIG. 19 shows a large form factor sputtering target prior to
compressing;
[0036] FIG. 20 shows a circular copper backing plate with loose
powder material incorporated into a central area of the plate;
and
[0037] FIG. 21 shows the circular copper backing plate of FIG. 20
after compression of the loose powder.
DETAILED DESCRIPTION
[0038] Mechanically-stable hermetic barrier layers can be formed by
physical vapor deposition (e.g., sputter deposition or laser
ablation) of a suitable starting material directly onto a workpiece
or onto a substrate that can be used to encapsulate a workpiece.
The starting materials include low T.sub.g glass materials and
their precursors, as well as polycrystalline or amorphous oxides of
copper or tin. As defined herein, a low T.sub.g glass material has
a glass transition temperature of less than 400.degree. C., e.g.,
less than 350, 300, 250 or 200.degree. C.
[0039] In embodiments, the number and size distribution of defects
that may be formed within the hermetic barrier layers are
constrained to a narrow specified range. By limiting the population
of defects, the as-formed layers through a self-passivation
mechanism can effectively compensate for such defects during
exposure to air or moisture and form a hermetic layer.
[0040] Example processes for forming hermetic barrier layers
include ion beam sputtering, magnetron sputtering, laser ablation,
remote plasma generation high target utilization sputtering (HiTUS)
and ion beam-assisted deposition (IBAD). Ion beam-assisted
deposition is a combination of two distinct physical operations,
physical vapor deposition of a target material onto a substrate and
simultaneous bombardment of the substrate surface with an ion beam.
Each of the foregoing approaches can be implemented in a batch or
continuous, e.g., roll-to-roll process. With each of these
techniques, the deposition rate of the barrier layer (low melting
temperature glass) material can be increased by increasing the
energy or flux of the corresponding ion or photon source. However,
such a pedestrian approach does not ensure that the defect
population within the formed layer will enable successful formation
of a hermetic barrier layer.
[0041] Embodiments relate to high-rate (e.g., greater than 10
A/sec) deposition of the hermetic barrier layers. The deposition
rate can be, for example, at least 10, 20, 50 or 100 A/sec.
High-rate deposition of hermetic barrier layers can be successfully
carried out by limiting the temperature of the target during
deposition, e.g., to less than 200.degree. C., and by constraining
the defect number and size distribution contributing to the barrier
layer's void space to be lower than what can be sealed from the
molar volume expansion accompanying passivation.
[0042] According to embodiments, hermetic barrier layers can be
formed using ion beam deposition processes. The ion beam-derived
layers can exhibit defect densities on the order of
2.times.10.sup.-2/cm.sup.2, which can be up to five orders of
magnitude less than the defect densities associated with most
magnetron sputtering approaches. Beneficial aspects of the ion beam
deposition approach, particularly in comparison to magnetron
sputtering, include a more directional flux (e.g., near normal
incidence), lower chamber background pressure, higher mean free
path, and the ability to independently adjust the ion flux energy
and power. Near-normal ion beam sputtering conditions have been
demonstrated to reduce the size of defects up to an order of
magnitude over off-normal sputtering conditions.
[0043] In the case of magnetron sputtering, a dominant source of
particle contamination is related to the finite cross-section of
the sputtering target surface that is exposed to weaker plasma
density. This non-homogeneous plasma density can cause the
formation, migration and mechanical ejection of filaments or
nodules (defects) from the target during deposition. Such a
defect-formation mechanism is undesirably exacerbated by applying
higher ion sputtering gas densities.
[0044] In embodiments, magnetron sputtering can be used to form
high deposition rate, high throughput, low defect density hermetic
barrier layers by, for instance, limiting the angular components of
the deposition process, for example through baffling, and/or by
using grounding grids in the deposition chamber.
[0045] In a similar vein, in the case of laser ablation, the
ejection of particulates with significant size occurs when the
photon flux is high enough to induce explosive ablation. When this
occurs, a highly-directed forward jet of target material
accompanies a broad-angle plume. The plume typically contains many
fine particles, from .about.0.01 .mu.m to 10 .mu.m, which are
ejected directly from the target surface.
[0046] In embodiments, the hermetic barrier layers are formed by a
non-equilibrium deposition process and have a defect size and
distribution where the volume in the layer occupied by as-deposited
defects is less than 15% of the total film volume after
self-passivation.
[0047] In conjunction with the instant methods, also disclosed are
approaches for preparing sputtering targets and associated
processing conditions for forming hermetic barrier layers from a
class of low melting temperature (i.e., low T.sub.g) glass
compositions. The barrier layers exhibit a self-passivating
attribute that results in layer that is hermetic to water and
oxygen.
[0048] Modeled data indicate that high-rate deposition can be
achieved by maintaining the sputtering target surface temperature
below 200.degree. C., e.g., below 180.degree. C. or 160.degree. C.
during deposition. The target temperature can be controlled, for
example, by sweeping processing plasma over a large area of the
target surface. Swept plasma limits the thermal load to any one
given target location despite a higher applied power and/or higher
ion flux, which can be used to accelerate the deposition rate.
Swept plasma may also result in better target utilization, with
more of the target material consumed in film formation. In contrast
to the disclosed approach, sputtering target surface temperatures
that exceed 200.degree. C. usually accompany a catastrophic failure
of the target, e.g., fracture of the target material, delamination
from the backing plate and/or evidence of significant chemical
attack.
[0049] Sweeping the plasma over the target surface can be performed
while actively cooling the target using, for example, a moving
magnet, rotating cylinder, or similar design. Ion beam flux designs
may similarly employ sweeping beams over cooled glass targets.
During the sputtering process, which is carried out within a vacuum
chamber, an internal pressure of the chamber can be less than
10.sup.-3 Torr, e.g., less than 1.times.10.sup.-3,
5.times.10.sup.-4 or 1.times.10.sup.-4 Torr.
[0050] FIG. 1 is a plot of magnetron sputter deposition rate versus
power for a sputtering target comprising a low T.sub.g tin
fluorophosphate glass. The data show results from swept plasma
(curve A) over a cooled (180-200.degree. C.) sputter target as well
as for a static, immobile plasma (curves B-E).
[0051] FIG. 2 is a plot of magnetron sputter deposition rate and
barrier layer uniformity versus distance from the substrate to the
target for a swept plasma over a cooled (180-200.degree. C.)
sputter target at 140 W.
[0052] Suitable deposition methods include non-equilibrium
processes such as ion beam sputtering, magnetron sputtering, and
laser ablation. Such non-equilibrium processes can be used to
ensure sufficient volumetric swelling of the barrier layer
material, but limit the expansion to less than 15%, e.g., less than
10%. By limiting the number and size distribution of defects within
the barrier layer to a narrow range, the volumetric expansion of
the material that occurs through reaction with moisture can
effectively pinch off pores and other defects to form a
self-passivated, hermetic barrier layer.
[0053] A variety of deposition apparatus can be used to form the
hermetic barrier layers. In accordance with an example embodiment,
a single-chamber sputter deposition apparatus 100 for forming such
barrier layers is illustrated schematically in FIG. 3. While the
apparatus and attendant methods are described below with respect to
deposition onto a substrate, it will be appreciated that the
substrate may be replaced by a workpiece or other device that is to
be protected by the barrier layer.
[0054] Apparatus 100 includes a vacuum chamber 105 having a
substrate stage 110 onto which one or more substrates 112 can be
mounted, and a mask stage 120, which can be used to mount shadow
masks 122 for patterned deposition of different layers onto the
substrates. The chamber 105 is equipped with a vacuum port 140 for
controlling the interior pressure, as well as a water cooling port
150 and a gas inlet port 160. The vacuum chamber can be cryo-pumped
(CTI-8200/Helix; MA, USA) and is capable of operating at pressures
suitable for both evaporation processes (.about.10.sub.-6 Torr) and
RF sputter deposition processes (.about.10.sub.-3 Torr).
[0055] As shown in FIG. 3, multiple evaporation fixtures 180, each
having an optional corresponding shadow mask 122 for evaporating
material onto a substrate 112, are connected via conductive leads
182 to a respective power supply 190. A target material 200 to be
evaporated can be placed into each fixture 180. Thickness monitors
186 can be integrated into a feedback control loop including a
controller 193 and a control station 195 in order to affect control
of the amount of material deposited.
[0056] In an example system, each of the evaporation fixtures 180
are outfitted with a pair of copper leads 182 to provide DC current
at an operational power of about 80-180 Watts. The effective
fixture resistance will generally be a function of its geometry,
which will determine the precise current and wattage.
[0057] An RF sputter gun 300 having a sputtering target 310 is also
provided for forming a barrier layer on a substrate. The RF sputter
gun 300 is connected to a control station 395 via an RF power
supply 390 and feedback controller 393. For sputtering inorganic,
hermetic layers, water-cooled cylindrical RF sputtering guns
(Onyx-3.TM., Onyx-R.TM., Angstrom Sciences, PA) can be positioned
within the chamber 105. Suitable RF deposition conditions include
50-150 W forward power (<1 W reflected power), which corresponds
to a typical deposition rate of about .about.5 .ANG./second
(Advanced Energy, Co, USA).
[0058] A post-deposition sintering or annealing step of the
as-deposited material may be performed or omitted. An optional
annealing step can reduce internal stresses within the barrier
layer.
[0059] In general, suitable materials for forming hermetic barrier
layers include low T.sub.g glasses and suitably reactive oxides of
copper or tin. Hermetic barrier layers can be formed from low
T.sub.g materials such as phosphate glasses, borate glasses,
tellurite glasses and chalcogenide glasses. Example borate and
phosphate glasses include tin phosphates, tin fluorophosphates and
tin fluoroborates. Sputtering targets can include such glass
materials or, alternatively, precursors thereof. Example copper and
tin oxides are CuO and SnO, which can be formed from sputtering
targets comprising pressed powders of these materials.
[0060] Optionally, the compositions can include one or more
dopants, including but not limited to tungsten, cerium and niobium.
Such dopants, if included, can affect, for example, the optical
properties of the barrier layer, and can be used to control the
absorption by the barrier material of electromagnetic radiation,
including laser radiation. For instance, doping with ceria can
increase the absorption by a low T.sub.g glass barrier at laser
processing wavelengths, which can enable the use of laser-based
sealing techniques after formation on a substrate or gasket.
[0061] Example tin fluorophosphate glass compositions can be
expressed in terms of the respective compositions of SnO, SnF.sub.2
and P.sub.2O.sub.5 in a corresponding ternary phase diagram.
Suitable tin fluorophosphates glasses include 20-100 mol % SnO,
0-50 mol % SnF.sub.2 and 0-30 mol % P.sub.2O.sub.5. These tin
fluorophosphates glass compositions can optionally include 0-10 mol
% WO.sub.3, 0-10 mol % CeO.sub.2 and/or 0-5 mol %
Nb.sub.2O.sub.5.
[0062] For example, a composition of a doped tin fluorophosphate
starting material suitable for forming a hermetic barrier layer
comprises 35 to 50 mole percent SnO, 30 to 40 mole percent
SnF.sub.2, 15 to 25 mole percent P.sub.2O.sub.5, and 1.5 to 3 mole
percent of a dopant oxide such as WO.sub.3, CeO.sub.2 and/or
Nb.sub.2O.sub.5.
[0063] A tin fluorophosphate glass composition according to one
particular embodiment is a niobium-doped tin oxide/tin
fluorophosphate/phosphorus pentoxide glass comprising about 38.7
mol % SnO, 39.6 mol % SnF.sub.2, 19.9 mol % P.sub.2O.sub.5 and 1.8
mol % Nb.sub.2O.sub.5. Sputtering targets that can be used to form
such a glass layer may include, expressed in terms of atomic mole
percent, 23.04% Sn, 15.36% F, 12.16% P, 48.38% O and 1.06% Nb.
[0064] A tin phosphate glass composition according to an alternate
embodiment comprises about 27% Sn, 13% P and 60% O, which can be
derived from a sputtering target comprising, in atomic mole
percent, about 27% Sn, 13% P and 60% O. As will be appreciated, the
various glass compositions disclosed herein may refer to the
composition of the deposited layer or to the composition of the
source sputtering target.
[0065] As with the tin fluorophosphates glass compositions, example
tin fluoroborate glass compositions can be expressed in terms of
the respective ternary phase diagram compositions of SnO, SnF.sub.2
and B.sub.2O.sub.3. Suitable tin fluoroborate glass compositions
include 20-100 mol % SnO, 0-50 mol % SnF.sub.2 and 0-30 mol %
B.sub.2O.sub.3. These tin fluoroborate glass compositions can
optionally include 0-10 mol % WO.sub.3, 0-10 mol % CeO.sub.2 and/or
0-5 mol % Nb.sub.2O.sub.5.
[0066] Typical prescriptions for managing thin film structure,
including the number and size of defects associated with thin film
deposition, are illustrated with a Thornton diagram (see FIG. 4).
The Thornton diagram shows deposited thin film morphological
regions arising from different sputtering gas pressure and
substrate temperature conditions, where microstructure is segmented
into zone I, zone T, zone II, and zone III morphologies. These
zones arise from different sputtering gas pressure and substrate
temperature conditions. Zone I films (low T.sub.S, high P.sub.G)
typically exhibit a microstructure of columnar crystallites 402
with voids in between the columns while zone II (high T.sub.S)
exhibits a microstructure of columnar grains 404 separated by
distinct dense inter-crystalline boundaries. Zone T (low T.sub.S,
low P.sub.G) is a transition zone in between zone I and II
consisting of a poorly-defined dense array of fibrous grains 406
without voided boundaries. A recrystallized grain structure 408 is
illustrated in Zone III.
[0067] Due to their relatively low melting temperature and chemical
liability, process conditions and the resulting layers that include
the glass compositions disclosed herein exhibit significant
deviation from typical refractory materials. For instance,
applicants have shown that the self-passivating character of
tin-containing glass compositions can be correlated to the
Sn.sup.2+ (i.e., SnO) content within the formed layer. Data show
that the Sn.sup.2+ content is a function of the substrate
temperature, and that Sn.sup.2+ rich layers can be formed by
cooling the substrate during deposition. At higher substrate
temperatures, lower amounts of Sn.sup.2+ are incorporated into the
barrier layer due to the loss of PO.sub.xF.sub.y and SnF.sub.x
species at the expense of Sn.sup.4+ (i.e., SnO.sub.2). Thin film
layers that incorporate a large fraction of Sn.sup.4+ do not
readily self-passivate and therefore do not form effective barrier
layers.
[0068] During formation of the barrier layer, the substrate can be
maintained at a temperature less than 200.degree. C., e.g., less
than 200, 150, 100, 50 or 23.degree. C. In embodiments, the
substrate is cooled to a temperature less than room temperature
during deposition of the barrier layer. The target temperature as
well as the substrate temperature can be controlled in both
ion-beam deposition processes and magnetron sputter deposition
processes.
[0069] FIG. 5 is a plot of barrier layer composition (wt. %) versus
deposition rate (A/sec) for increasing values of magnetron sputter
power (50, 70, 90 or 110 Watts). The initial sputtering target
composition included 49.2 wt. % oxygen, 23.0 wt. % tin, 14.5 wt. %
fluorine, 12.3 wt. % phosphorus and 1.0 wt. % Nb. The filled data
points correspond to a substrate temperature of 45.degree. C.,
while the open data points correspond to a substrate temperature of
15.degree. C. The sputtering target temperature was maintained less
than 200.degree. C.
[0070] FIG. 6 is a corresponding plot of percentage Sn.sup.4+
(i.e., Sn.sup.4+/total Sn content) versus deposition rate. As with
FIG. 5, the filled data points correspond to a substrate
temperature of 45.degree. C., while the open data points correspond
to a substrate temperature of 15.degree. C. The FIG. 6 data clearly
show that the Sn.sup.4+ content in the barrier layers can be
advantageously suppressed by cooling the substrate.
[0071] Additional aspects of suitable low T.sub.g glass
compositions and methods used to form glass layers from these
materials are disclosed in commonly-assigned U.S. Pat. No.
5,089,446 and U.S. patent application Ser. Nos. 11/207,691,
11/544,262, 11/820,855, 12/072,784, 12/362,063, 12/763,541 and
12/879,578, the entire contents of which are incorporated by
reference herein.
[0072] The hermetic barrier layer materials disclosed herein may
comprise a binary, ternary or higher-order composition. A survey of
several binary oxide systems reveals other materials capable of
forming self-passivating hermetic barrier layers. In the copper
oxide system, for example, as-deposited amorphous CuO reacts with
moisture/oxygen to partially form crystalline Cu.sub.4O.sub.3 and
the resulting composite layer exhibits good hermeticity. When
Cu.sub.2O is deposited as the first inorganic layer, however, the
resulting film is not hermetic. In the tin oxide system,
as-deposited amorphous SnO reacts with moisture/oxygen to partially
form crystalline Sn.sub.6O.sub.4(OH).sub.4 and SnO.sub.2. The
resulting composite layer exhibits good hermeticity. When SnO.sub.2
is deposited as the first inorganic layer, however, the resulting
film is not hermetic.
[0073] According to various sputtering approaches, a
self-passivating layer can be formed on a surface of a substrate or
workpiece from a suitable target material. The self-passivating
layer is an inorganic material. Without wishing to be bound by
theory, it is believed that, according to various embodiments,
during or after its formation, the as-deposited layer reacts with
moisture or oxygen to form a mechanically-stable hermetic barrier
layer. The hermetic barrier layer comprises the as-deposited layer
and a second inorganic layer, which is the reaction product of the
deposited layer with moisture or oxygen. Thus, the second inorganic
layer forms at the ambient interface of the as-deposited layer. A
schematic of a hermetic barrier layer 704 formed over a surface of
a substrate 700 is illustrated in FIG. 7. In the illustrated
embodiment, the hermetic barrier layer 704 comprises a first
(as-deposited) inorganic layer 704A, and a second (reaction
product) inorganic layer 704B. In embodiments, the first and second
layers can cooperate to form a composite thin film that can isolate
and protect an underlying structure. The passivatable as-deposited
layer comprises a low T.sub.g glass material or an oxide of copper
or tin
[0074] According to further embodiments, a molar volume of the
passivated second inorganic layer material is from about 1% to 15%
greater than a molar volume of the first inorganic layer material,
and an equilibrium thickness of the second inorganic layer is at
least 10% of but less than an initial thickness of the first
inorganic layer. While the first inorganic layer can be amorphous,
the second inorganic layer can be at least partially
crystalline.
[0075] In embodiments, the molar volume change (e.g., increase)
manifests as a compressive force within the composite barrier layer
that contributes to a self-sealing phenomenon. Because the second
layer is formed as the spontaneous reaction product of the first
inorganic layer with oxygen or water, as-deposited layers (first
inorganic layers) that successfully form hermetic barrier layers
are less thermodynamically stable than their corresponding second
inorganic layers. Thermodynamic stability is reflected in the
respective Gibbs free energies of formation.
[0076] The hermetic barrier layers disclosed herein may be
characterized as thin film materials. A total thickness of a
hermetic barrier layer can range from about 150 nm to 200 microns.
In various embodiments, a thickness of the as-deposited layer can
be less than 200 microns, e.g., less than 200, 100, 50, 20, 10, 5,
2, 1, 0.5 or 0.2 microns. Example thicknesses of as-deposited glass
layers include 200, 100, 50, 20, 10, 5, 2, 1, 0.5, 0.2 or 0.15
microns.
[0077] Hermetic barrier layers formed by physical vapor deposition
according to the present disclosure may exhibit a self-passivating
attribute that efficiently and significantly impedes moisture and
oxygen diffusion.
[0078] According to embodiments, the choice of the hermetic barrier
layer material(s) and the processing conditions for forming
hermetic barrier layers over a workpiece or substrate are
sufficiently flexible that the workpiece or substrate is not
adversely affected by formation of the barrier layer.
[0079] Example sputtering configurations according to various
embodiments are illustrated in FIGS. 8 and 9. FIG. 8 shows RF
sputtering from a sputtering target 310 to form a barrier layer on
a substrate 112 that is supported by a rotating substrate stage 110
as also depicted in FIG. 3. FIG. 9 shows a portion of an in-line
planar magnetron sputtering apparatus configured to continuously
form a hermetic barrier layer on a surface of a translating
substrate. A direction of motion of the substrate is shown in FIG.
9 by arrow A. The pristine substrate can be unwrapped from a first
roll, passed over a deposition zone of the magnetron sputtering
target 311 to provide a barrier layer on a portion of the
workpiece, and then the coated workpiece can be wrapped onto a
second roll.
[0080] A hermetic layer is a layer which, for practical purposes,
is considered substantially airtight and substantially impervious
to moisture and/or oxygen. By way of example, the hermetic thin
film can be configured to limit the transpiration (diffusion) of
oxygen to less than about 10.sup.-2 cm.sup.3/m.sup.2/day (e.g.,
less than about 10.sup.-3 cm.sup.3/m.sup.2/day), and limit the
transpiration (diffusion) of water to about 10.sup.-2 g/m.sup.2/day
(e.g., less than about 10.sup.-3, 10.sup.-4, 10.sup.-5 or 10.sup.-6
g/m.sup.2/day). In embodiments, the hermetic thin film
substantially inhibits air and water from contacting an underlying
workpiece or a workpiece sealed within a structure using the
hermetic material.
[0081] To evaluate the hermeticity of the hermetic barrier layers,
calcium patch test samples were prepared using the single-chamber
sputter deposition apparatus 100. In a first step, calcium shot
(Stock # 10127; Alfa Aesar) was evaporated through a shadow mask
122 to form 25 calcium dots (0.25 inch diameter, 100 nm thick)
distributed in a 5.times.5 array on a 2.5 inch square glass
substrate. For calcium evaporation, the chamber pressure was
reduced to about 10.sup.-6 Torr. During an initial pre-soak step,
power to the evaporation fixtures 180 was controlled at about 20 W
for approximately 10 minutes, followed by a deposition step where
the power was increased to 80-125 W to deposit about 100 nm thick
calcium patterns on each substrate.
[0082] Following evaporation of the calcium, the patterned calcium
patches were encapsulated using comparative inorganic oxide
materials as well as hermetic inorganic oxide materials according
to various embodiments. The inorganic oxide materials were
deposited using room temperature RF sputtering of pressed powder or
glass sputtering targets. The pressed powder targets were prepared
separately using a manual heated bench-top hydraulic press (Carver
Press, Model 4386, Wabash, Ind., USA). The press was typically
operated at 5,000 psi for 2 hours at about 200.degree. C.
[0083] The RF power supply 390 and feedback control 393 (Advanced
Energy, Co, USA) were used to form first inorganic oxide layers
over the calcium having a thickness of about 2 micrometers. No
post-deposition heat treatment was used. Chamber pressure during RF
sputtering was about 1 milliTorr. The formation of a second
inorganic layer over the first inorganic layer was initiated by
ambient exposure of the test samples to room temperature and
atmospheric pressure prior to testing.
[0084] FIG. 10 is a cross-sectional view of a test sample
comprising a glass substrate 900, a patterned calcium patch
(.about.100 nm) 902, and an inorganic oxide film (.about.2 .mu.m)
904. Following ambient exposure, the inorganic oxide film 904
comprises a first inorganic layer 904A and a second inorganic layer
904B. In the illustrated embodiment, the second inorganic layer is
formed over a major surface of the first inorganic layer. In a
non-illustrated embodiment, the second inorganic layer may also be
formed over the exposed edges (side surfaces) of the first
inorganic layer. In order to evaluate the hermeticity of the
inorganic oxide film, calcium patch test samples were placed into
an oven and subjected to accelerated environmental aging at a fixed
temperature and humidity, typically 85.degree. C. and 85% relative
humidity ("85/85 testing").
[0085] The hermeticity test optically monitors the appearance of
the vacuum-deposited calcium layers. As-deposited, each calcium
patch has a highly reflective metallic appearance. Upon exposure to
water and/or oxygen, the calcium reacts and the reaction product is
opaque, white and flaky. Survival of the calcium patch in the 85/85
oven over 1000 hours is equivalent to the encapsulated film
surviving 5-10 years of ambient operation. The detection limit of
the test is approximately 10.sup.-7 g/m.sup.2 per day at 60.degree.
C. and 90% relative humidity.
[0086] FIG. 11 illustrates behavior typical of non-hermetically
sealed and hermetically sealed calcium patches after exposure to
the 85/85 accelerated aging test. In FIG. 11, the left column shows
non-hermetic encapsulation behavior for Cu.sub.2O films formed
directly over the patches. All of the Cu.sub.2O-coated samples
failed the accelerated testing, with catastrophic delamination of
the calcium dot patches evidencing moisture penetration through the
Cu.sub.2O layer. The right column shows positive test results for
nearly 50% of the samples comprising a CuO-deposited hermetic
layer. In the right column of samples, the metallic finish of 34
intact calcium dots (out of 75 test samples) is evident.
[0087] Both glancing angle x-ray diffraction (GIXRD) and
traditional powder x-ray diffraction were used to evaluate the near
surface and entire oxide layer, respectively, for both non-hermetic
and hermetic deposited layers. FIG. 12 shows GIXRD data (plots A
and C) and traditional powder reflections (plots B and D) for both
hermetic CuO-deposited layers (plots A and B) and non-hermetic
Cu.sub.2O-deposited layers (plots C and D). Typically, the 1 degree
glancing angle used to generate the GIXRD scans of FIGS. 12A and 4C
probes a near-surface depth of approximately 50-300 nanometers.
[0088] Referring still to FIG. 12, the hermetic CuO-deposited film
(plot A) exhibits near surface reflections that index to the phase
paramelaconite (Cu.sub.4O.sub.3), though the interior of the
deposited film (plot B) exhibits reflections consistent with a
significant amorphous copper oxide content. The paramelaconite
layer corresponds to the second inorganic layer, which formed from
the first inorganic layer (CuO) that was formed directly over the
calcium patches. In contrast, the non-hermetic Cu.sub.2O-deposited
layer exhibits x-ray reflections in both scans consistent with
Cu.sub.2O.
[0089] The XRD results suggest that hermetic films exhibit a
significant and cooperative reaction of the sputtered
(as-deposited) material with heated moisture in the near surface
region only, while non-hermetic films react with heated moisture in
their entirety yielding significant diffusion channels which
preclude effective hermeticity. For the copper oxide system, the
hermetic film data (deposited CuO) suggest that paramelaconite
crystallite layer forms atop an amorphous base of un-reacted
sputtered CuO, thus forming a mechanically stable and hermetic
composite layer.
[0090] FIGS. 13A-13H show a series of GIXRD plots, and FIG. 13I
shows a Bragg XRD spectrum for a CuO-deposited hermetic barrier
layers following accelerated testing. Bragg diffraction from the
entire film volume has an amorphous character, with the
paramelaconite phase present at/near the film's surface. Using a
CuO density of 6.31 g/cm.sup.3, a mass attenuation coefficient of
44.65 cm.sup.2/g, and an attenuation coefficient of 281.761
cm.sup.-1, the paramelaconite depth was estimated from the GIXRD
plots of FIG. 13. In FIGS. 13A-13H, successive glancing incident
x-ray diffraction spectra obtained at respective incident angles of
1.degree., 1.5.degree., 2.degree., 2.5.degree., 3.0.degree.,
3.5.degree., 4.degree., and 4.5.degree. show a surface layer
(paramelaconite) that comprises between 31% (619 nm) and 46% (929
nm) of the original 2 microns of sputtered CuO after exposure to
85.degree. C. and 85% relative humidity for 1092 hours. A summary
of the calculated surface depth (probed depth) for each GIXRD angle
is shown in Table 1.
TABLE-US-00001 TABLE 1 Paramelaconite depth profile FIG. GIXRD
angle (degrees) Probed Depth (nm) 13A 1 300 13B 1.5 465 13C 2 619
13D 2.5 774 13E 3 929 13F 3.5 1083 13G 4 1238 13H 4.5 1392 13I n/a
2000
[0091] In addition to the hermeticity evaluations conducted using
copper oxide-based barrier layers, tin oxide-based barrier layers
were also evaluated. As seen with reference to FIG. 14, which shows
GIXRD spectra for SnO (top) and SnO.sub.2-deposited films (bottom)
after 85/85 exposure, the hermetic thin film (top) exhibits a
crystalline SnO.sub.2-like (passivation) layer that has formed over
the deposited amorphous SnO layer, while the non-hermetic
(SnO.sub.2-deposited) film exhibits an entirely crystalline
morphology.
[0092] Table 2 highlights the impact of volume change about the
central metal ion on the contribution to film stress of the surface
hydration products. It has been discovered that a narrow band
corresponding to an approximate 15% or less increase in the molar
volume change contributes to a hermetically-effective compressive
force. In embodiments, a molar volume of the second inorganic layer
is from about -1% to 15% (i.e., -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
10, 11, 12, 13, 14 or 15%) greater than a molar volume of the first
inorganic layer. The resulting self-sealing behavior (i.e.,
hermeticity) appears related to the volume expansion.
TABLE-US-00002 TABLE 2 Calculated Molar Volume Change for Various
Materials Sputtering Target .DELTA. Molar Material/First Second
Volume Hermetic Inorganic Layer Inorganic Layer [%] Layer? SnO
SnO.sub.2 5.34 yes FeO Fe.sub.2O.sub.3 .sup..dagger. 27.01 no
Sb.sub.2O.sub.3 Sb.sub.2O.sub.5 .sup..dagger. 63.10 no
(senarmonitite) Sb.sub.2O.sub.3 Sb.sub.2O.sub.5 .sup..dagger. 67.05
no (valentinite) Sb.sub.2O.sub.3 Sb + 3Sb + 5O.sub.4 -9.61 no
(valentinite) (cervantite) Sb.sub.2O.sub.3 Sb.sub.3O.sub.6(OH)
-14.80 no (valentinite) (stibiconite) .sup..dagger. Ti.sub.2O.sub.3
TiO.sub.2 .sup..dagger. 17.76 no Cu.sub.2O
Cu.sup.+.sub.2Cu.sup.2+.sub.2O.sub.3 12.30 no (paramelaconite)
.sup..dagger. CuO Cu.sup.+.sub.2Cu.sup.2+.sub.2O.sub.3 0.97 yes
(paramelaconite) .sup..dagger. estimate
[0093] Table 3 shows the hermetic-film-forming inorganic oxide was
always the least thermodynamically stable oxide, as reflected in
its Gibbs free energy of formation, for a given elemental pair.
This suggests that as-deposited inorganic oxide films are
metastable and thus potentially reactive towards hydrolysis and/or
oxidation.
TABLE-US-00003 TABLE 3 Gibbs Formation Free Energy
(.DELTA.G.degree..sub.formation) of Various Oxides Target Material
.DELTA.G.degree..sub.formation [kJ/mol] Hermetic Layer SnO -251.9
yes SnO.sub.2 -515.8 no CuO -129.7 yes Cu.sub.2O -146.0 no
[0094] In embodiments, the barrier layer can be derived from room
temperature sputtering of one or more of the foregoing materials,
though other thin film deposition techniques can be used. In order
to accommodate various workpiece architectures, deposition masks
can be used to produce a suitably patterned hermetic barrier layer.
Alternatively, conventional lithography and etching techniques can
be used to form a patterned hermetic layer from a
previously-deposited blanket layer.
[0095] To form hermetic barrier layers via sputtering, a sputtering
target may comprise a low T.sub.g glass material or a precursor
thereof, such as a pressed powder target where the powder
constituents have an overall composition corresponding to the
desired barrier layer composition. Glass-based sputtering targets
may comprise a dense, single phase low T.sub.g glass material.
Aspects of forming both glass composition sputtering targets and
pressed powder sputtering targets are disclosed herein.
[0096] For both glass composition and pressed powder composition
targets, a thermally-conductive backing plate such as a copper
backing plate may be used to support the target material. The
backing plate can have any suitable size and shape. In one example
embodiment, a 3 inch outer diameter (OD) circular copper backing
plate is formed from a 0.25 inch thick copper plate. A central area
having a diameter of about 2.875 inch is milled from the plate to a
depth of about 1/8 inch, leaving an approximately 1/16 inch wide
lip around a peripheral edge of the central area. A photograph of
such a copper backing plate is shown in FIG. 15.
[0097] To form a glass composition sputtering target according to
one embodiment, the central area of the backing plate is initially
coated with a thin layer of flux-less solder (Cerasolzer ECO-155).
The solder provides an oxide-free, or substantially oxide-free,
adhesion-promoting layer to which the target material can be
bonded. An image of a solder-treated copper backing plate is shown
in FIG. 16.
[0098] A desired glass composition can be prepared from raw
starting materials. Starting materials to form a tin
fluorophosphate glass, for example, can be mixed and melted to
homogenize the glass. The raw materials, which can comprise powder
materials, can be heated, for example, in a carbon crucible to a
temperature in the range of 500-550.degree. C., and then cast onto
a graphite block to form a glass cullet. The cullet can be broken
up, remelted (500-550.degree. C.), and then poured into the central
area of a pre-heated, solder-treated backing plate. The backing
plate can be pre-heated to a temperature in the range of
100-125.degree. C. The casting can be annealed at a temperature of
100-125.degree. C. for 1 hour, though longer anneal times can be
used for larger backing plates. An image of an as-annealed low
T.sub.g glass sputtering target is shown in FIG. 17.
[0099] After the glass composition is annealed, the glass can be
heat-pressed against the solder-coated copper, e.g., using a Carver
press at a temperature of below 225.degree. C., e.g., from
140-225.degree. C. and an applied pressure of 2000-25,000 psi. The
heat-pressing promotes thorough compaction and good adhesion of the
glass material to the backing plate. In a further embodiment, the
step of heat-pressing can be performed at a temperature of less
than 180.degree. C. An image of a pressed, low T.sub.g glass
sputtering target is shown in FIG. 18.
[0100] By controlling the temperature and pressure used to anneal
and compress the glass target, the formation of unwanted voids or
secondary phases can be minimized or avoided. In accordance with
various embodiments, a sputtering target comprising a low T.sub.g
glass material can have a density approaching or equal to the
theoretical density of the glass material. Example target materials
include glass material having a density greater than 95% of a
theoretical density of the material (e.g., at least 96, 97, 98, or
99% dense).
[0101] By providing dense sputtering targets, degradation of the
target during use can be minimized. For instance, the exposed
surface of a target that contains porosity or mixed phases may
become preferentially sputtered and roughened during use as the
porosity or second phase is exposed. This can result in a runaway
degradation of the target surface. A roughened target surface may
lead to flaking of particulate material from the target, which can
lead to the incorporation of defects or particle occlusions in the
deposited layer. A barrier layer comprising such defects may be
susceptible to hermetic breakdown. Dense sputtering targets may
also exhibit uniform thermal conductivity, which promotes
non-destructive heating and cooling of the target material during
operation.
[0102] According to various embodiments, methods for forming a
sputtering target disclosed herein can be used to produce single
phase, high density targets of a low T.sub.g glass composition. The
glass targets can be free of secondary or impurity phases. While
the foregoing relates to forming a sputtering target directly on a
backing plate, it will be appreciated that a suitable glass-based
target composition can be prepared independently from such a
backing plate and then optionally incorporated onto a backing plate
in a subsequent step.
[0103] In embodiments, a method of making a sputtering target
comprising a low T.sub.g glass material comprises providing a
mixture of raw material powders, heating the powder mixture to form
a molten glass, cooling the glass to form a cullet, melting the
cullet to form a glass melt, and shaping the glass melt into a
solid sputtering target. FIG. 19 is an image showing the
incorporation of glass material into the central area of larger
form factor rectangular backing plate.
[0104] As an alternative to a glass material-based sputtering
target, the steps of melting and homogenizing the starting raw
materials can be omitted, and instead powder raw materials can be
mixed and pressed directly into the central area of a suitable
backing plate. FIG. 20 is an image showing the incorporation of
powder raw materials into the central area of a circular backing
plate, and FIG. 21 shows a final pressed-powder sputtering target
after compression of the powder materials of FIG. 20.
[0105] A method of making a pressed-powder sputtering target
comprising a powder compact having the composition of a low T.sub.g
glass comprises providing a mixture of raw material powders, and
pressing the mixture into a solid sputtering target. In such an
approach, the powder mixture is a precursor of a low T.sub.g glass
material. In a related approach, a method of making a
pressed-powder sputtering target comprising an oxide of copper or
tin comprises providing a powder of CuO or SnO and pressing the
powder into a solid sputtering target.
[0106] Hermetic barrier layers formed by sputtering may be
optically transparent, which make them suitable for encapsulating,
for example, food items, medical devices, and pharmaceutical
materials, where the ability to view the package contents without
opening the package may be advantageous. Optical transparency may
also be useful in sealing opto-electronic devices such as displays
and photovoltaic devices, which rely on light transmission. In
embodiments, the hermetic barrier layers have an optical
transparency characterized by an optical transmittance of greater
than 90% (e.g., greater than 90, 92, 94, 96 or 98%).
[0107] In one further example embodiment, sputter-deposited
hermetic barrier layers may be used to encapsulate a workpiece that
contains a liquid or a gas. Such workpieces include dye-sensitized
solar cells (DSSCs), electro-wetting displays, and electrophoretic
displays. The disclosed hermetic barrier layers can substantially
inhibit exposure of a workpiece to air and/or moisture, which can
advantageously prevent undesired physical and/or chemical reactions
such as oxidation, hydration, absorption or adsorption,
sublimations, etc. as well as the attendant manifestations of such
reactions, including spoilage, degradation, swelling, decreased
functionality, etc.
[0108] Due to the hermeticity of the protective barrier layer, the
lifetime of a protected workpiece can be extended beyond that
achievable using conventional hermetic barrier layers. Other
devices that can be protected using the disclosed materials and
methods include organic LEDs, fluorophores, alkali metal
electrodes, transparent conducting oxides, and quantum dots.
[0109] Disclosed are sputtering targets and methods for forming
sputtering targets that comprise a low T.sub.g glass material or
precursor thereof, or an oxide of copper or tin. Sputtering
processes using the foregoing targets can be used to form
self-passivating hermetic barrier layers.
[0110] As used herein, the singular forms "a," "an" and "the"
include plural referents unless the context clearly dictates
otherwise. Thus, for example, reference to a "glass" includes
examples having two or more such "glasses" unless the context
clearly indicates otherwise.
[0111] Ranges can be expressed herein as from "about" one
particular value, and/or to "about" another particular value. When
such a range is expressed, examples include from the one particular
value and/or to the other particular value. Similarly, when values
are expressed as approximations, by use of the antecedent "about,"
it will be understood that the particular value forms another
aspect. It will be further understood that the endpoints of each of
the ranges are significant both in relation to the other endpoint,
and independently of the other endpoint.
[0112] Unless otherwise expressly stated, it is in no way intended
that any method set forth herein be construed as requiring that its
steps be performed in a specific order. Accordingly, where a method
claim does not actually recite an order to be followed by its steps
or it is not otherwise specifically stated in the claims or
descriptions that the steps are to be limited to a specific order,
it is no way intended that any particular order be inferred.
[0113] It is also noted that recitations herein refer to a
component being "configured" or "adapted to" function in a
particular way. In this respect, such a component is "configured"
or "adapted to" embody a particular property, or function in a
particular manner, where such recitations are structural
recitations as opposed to recitations of intended use. More
specifically, the references herein to the manner in which a
component is "configured" or "adapted to" denotes an existing
physical condition of the component and, as such, is to be taken as
a definite recitation of the structural characteristics of the
component.
[0114] It will be apparent to those skilled in the art that various
modifications and variations can be made to the present invention
without departing from the spirit and scope of the invention. Since
modifications, combinations, sub-combinations and variations of the
disclosed embodiments incorporating the spirit and substance of the
invention may occur to persons skilled in the art, the invention
should be construed to include everything within the scope of the
appended claims and their equivalents.
* * * * *